A data consists of $n$ observations

${x_1},{x_2},......,{x_n}.$ If $\sum\limits_{i - 1}^n {{{({x_i} + 1)}^2}}  = 9n$ and $\sum\limits_{i - 1}^n {{{({x_i} - 1)}^2}}  = 5n,$ then the standard deviation of this data is

  • [JEE MAIN 2019]
  • A

    $5$

  • B

    $\sqrt 5$

  • C

    $\sqrt 7$

  • D

    $2$

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